Gelled emulsion products containing chitosan

ABSTRACT

A sterilized, gelled emulsion product which contains protein, lipid, carbohydrate and a binder. The binder is made up of chitosan or a mixture of chitosan and a polyphosphate. The emulsion product is less susceptible to cook out of fats and starch during sterilization and has a firm, relatively elastic texture. The sterilized, gelled emulsion product may be provided in the form of a chunks-in-liquid pet food.

This invention relates to a gelled and sterilized emulsion product; forexample meat or fish analogues. The invention also relates to a processfor preparing the gelled emulsion product and to the use of chitosan asa binder for the gelled emulsion products.

Gelled emulsion products are commonly used as foodstuffs. This isespecially the case in the pet food industry where they are used as meator fish analogues. However they are also used in other fields such asthe sausage field. In the pet food industry, these products are usuallyprovided in cans and in one of two forms; loaf type products andchunk-type products.

The loaf type products are usually prepared by comminuting meat or fishmaterial and mixing the material with other protein sources and fats, ifnecessary, and water, salt, spices, curing agents, gelling agents toprovide a batter. The batter is then heated. The heated batter is thenfilled into cans to form, after retorting and cooling, a meat or fishloaf.

The chunk-type products may be produced in a similar manner; the primarydifference being the selection of specific gelling agents to provide aharder, tougher structure. For example, as described in European patentapplication 001 8153, a gelling system made up of a carrageenan and aglucomannan may be used to prepare chunks-type products. The componentsmaking up product are mixed together, heated to above 100° C. to form agel, filled into cans, and then sterilized at 130° C. for 50 to 60minutes.

Alternatively, the chunk-type products may be produced in the form offormulated emulsions which closely simulate the appearance of meat orfish. One example of a process for producing these formulated emulsionsis described in U.S. Pat. No. 4,781,939. Here, a viscous emulsion isprepared from meat, proteinaceous materials (for example wheat glutenand soy flour), vitamins, minerals and the like. The viscous emulsion isthen run through a high-speed emulsion mill in which the emulsion israpidly heated. The emulsion leaving the emulsion mill is then allowedto coagulate to form a solid emulsion product. This solid emulsionproduct is then cut into chunks. A similar process is described in U.S.Pat. No. 5,132,137.

In all cases, once the emulsion products have been filled into cans, thecans are subjected to retorting to sterilize the emulsion products. Theretorting operation is severe with temperatures up to 130° C. beingreached for relatively long periods of time. This may result in releaseof fats and starch from the emulsion product; a phenomenon known as“cook out”. The phenomenon is particularly prevalent in emulsionproducts with a high water content. If cook out occurs, the appearanceof the product is adversely affected; often to a significant extent.This may greatly reduce consumer acceptability.

Therefore, it is an object of this invention to provide an emulsionproduct with reduced susceptibility to cook out. Accordingly, in oneaspect, this invention provides a sterilized, gelled emulsion productcontaining protein, lipid, carbohydrate and a binder; the bindercomprising chitosan. Preferably the gelled emulsion product is providedin the form of chunks in a liquid. The liquid may be a sauce or gravy.

Surprisingly, gelled emulsion products in which the binder compriseschitosan are able to withstand normal sterilization procedures withlimited cook out of lipids and starch. This remains the case even forproducts with relatively high concentrations of lipids. Further, thegelled emulsion products have improved texture in that they exhibitimproved firmness and have good elasticity.

Preferably the binder further comprises a food grade polyphosphate; forexample a sodium diphosphate.

In another aspect, this invention provides a process for producing asterilized, gelled emulsion product, the process comprising:

forming an emulsion containing protein, lipid, and carbohydrate;

adding a binder, which includes chitosan, to the emulsion;

heating the emulsion to above about 65° C. to cause the emulsion to gel;

forming the gelled emulsion into chunks;

filling the chunks and a liquid into containers; and

sterilizing the containers at above about 120° C. to provide thesterilized, gelled emulsion product.

In further aspect, this invention provides the use of chitosan and afood grade polyphosphate as a binder in the preparation of a sterilized,gelled emulsion product.

Embodiments of the invention are now described, by way of example only.The invention provides a sterilized, gelled emulsion product thatcontains protein, lipid, carbohydrate and a binder.

The protein may be provided in the form of a meat material, animal ordiary proteins, and vegetable proteins, or mixtures of these. Anysuitable type of meat material may be used, for example, muscular orskeletal meat, meat by-products such as hearts, liver, kidneys, tongue,or a mixture of meat and meat by-products. Further, the material may beobtained from any suitable source such as from livestock, poultry, andfish. Also, the meat material may be in the form of meat meals such aspoultry meal, fish meal, red meat meal and mixtures thereof. Suitableanimal or dairy proteins which may be used include egg proteins,gelatin, whey, and casein, or mixtures of these. Suitable vegetableproteins which may be used include wheat gluten, soy flour, soy proteinconcentrates, soy protein isolates, pea protein isolates, etc, ormixtures of these. The exact choice of protein used will depend uponfactors such as availability, cost and palatability. Typically, theprotein comprises about 5% to about 15% by weight of the gelled emulsionproduct.

The lipid may be provided in the form of suitable animal or vegetablefats and oils, or both. If the protein is provided in the form of a meatmaterial, the meat material may well provide the desired amount oflipids and hence addition of further lipid may not be necessary.Suitable examples of animal fats are tallow, chicken fats, pork fats,beef fats, and the like. Suitable examples of vegetable fats and oilsare hydrogenated palm oil, corn oil, sunflower oil, rapeseed oil, andthe like.

Typically the emulsion product contains a maximum lipid level of about25% by weight. Conveniently, the amount of lipid in the emulsion is inthe range of about 2% to 15% by weight; more preferably about 5% toabout 12% by weight.

The carbohydrate is preferably provided in the form of a starch orflour. Suitable carbohydrate sources are wheat starch, potato starch,corn starch, wheat flour, corn flour, oat flour, rye flour, rice flour,and the like. Sugars may also be added. Typically, the carbohydrate, inthe form of starch or flour, comprises about 3% to about 15% by weightof the gelled emulsion product.

Additional ingredients such as salts, spices, seasonings, flavoringagents, minerals, and the like may also be included in the emulsionproduct. The amount of additional ingredients used is preferably suchthat they make up about 0.5% to about 5% by weight of the emulsionproduct.

The binder includes chitosan. The chitosan preferably comprises about0.05% to about 2% by weight of the emulsion product; more preferablyabout 0.1% to about 1% by weight. Further, in addition to the chitosan,the binding agent preferably includes a food grade polyphosphate; forexample a diphosphate such as Na₄P₂O₇. The polyphosphate preferablycomprises about 0.05% to about 2% by weight of the emulsion product;more preferably about 0.1% to about 1% by weight.

The emulsion product may be prepared by emulsifying the protein,carbohydrates and lipids to provide a primary emulsion. The additionalingredients such as salts, spices, seasonings, flavoring agents,minerals, and the like may be added at this time. Water may also beincluded in the primary emulsion to provide from about 50% to about 90%by weight of the primary emulsion. If sufficient moisture is present inthe protein, especially if the protein is provided as a meat material,water need not be added. A higher speed emulsifier or homogeniser isparticularly suitable for preparing the primary emulsion.

If a polyphosphate is used in the binder, the polyphosphate is thenadded to the primary emulsion and allowed to react with the protein. Thereaction time may be varied as desired but may be in the range of about2 minutes to about 24 hours.

The chitosan is then added to the primary emulsion; preferably insolution. The primary emulsion is then subjected to further mixing oremulsification. The primary emulsion is then heated to a temperatureabove about 65° C.; for example in a mixer-cooker. Steam may be injectedinto the primary emulsion if desired.

If it is desired to produce chunks, the heated emulsion may then beextruded, cooled and cut into chunks. Alternatively, formulated emulsionchunks may be produced by rapidly heating the primary emulsion in anemulsion mill as described in U.S. Pat. Nos. 4,781,939 and 5,132,137;the disclosures of which are incorporated by reference. The chunks maythen be mixed with a suitable liquid, such as a gravy or jelly andfilled into cans or other containers. The gravy or sauce may be producedfrom water, starch, suitable flavoring agents and optionally gums.

However, if it desired to produce a loaf type product, the heatedemulsion may be filled directly into cans or other containers. The cansor other containers are then sealed and sterilized. Sterilizationusually takes place at a temperature above about 120° C. and for aperiod of at least about 15 minutes.

The gelled emulsion product obtained undergoes much less cook out offats and starches giving a product with an excellent appearance.Further, the gelled emulsion product has a firm, relatively elastictexture.

Specific examples are now described for further illustration.

EXAMPLE 1

Frozen pork shoulder and foreleg is comminuted and emulsified with porkback fat in a homogenizer. Carbohydrate, in the form of wheat starch,and salt are added and the mixture mixed at low speed. Water is addedand the mixture emulsified at high speed.

The mixture is divided into two parts. Chitosan (Seacure CL3 13 obtainedfrom Pronova A/S of Norway) is dissolved in water to provide a 2% to 3%by weight solution. The chitosan has a percentage deacetylation of 83%and pH of 4.5. The chitosan solution is added to one part of themixture; the other part forming a control. The mixtures are heatedtreated at 78° C. for 30 minutes and then allowed to cool to form gelledemulsion products. The components used to produce each gelled emulsionproduct are as follows:

Meat Fat Starch Chitosan Salt Added Product % % % % % Water % 1 35 12 100.5 2 40.5 Control A 35 12 10 — 2 41

The gelled emulsion products are cut into chunks and filled into canswith water. The cans are sealed and sterilized at 121° C. for 20minutes. The cans are then allowed to cool.

The cans are opened and the contents visually inspected. The chunks ofproduct 1 are well-formed chunks with well defined edges. Little or nocook out of fat or starch is noticeable. The chunks of control product Ahave less well defined edges. Cook out of fat and starch is readilynoticeable.

A sample chunk is taken from each product and cut into a piece of 15 mmby 15 mm by 25 mm. The fracture properties of each piece is thenanalyzed using a Instron 1122 machine at a constant crosshead speed of20 mm per minute. The stress and strain values obtained are as follows:

Stress at fracture Strain at Product (kPa) fracture 1 3.5 0.115 ControlA 2.4 0.105

Product 1 has a higher stress value than the control product indicatingthat it is firmer. Further, product 1 has a higher strain value than thecontrol product indicating that it is more elastic.

A further sample chunk is taken from each product and is frozen usingliquid nitrogen. Sections of 20 μm are made from each sample chunk. Thesections are mounted on glass slides and stored until stained. Half ofthe sections are stained using a solution of Aniline blue and Orange Gto colour collagen and gelatin blue and myofibrillar protein yellow.Starches and fats are uncolored. The other half of the sections arestained using an iodine solution to colour amylose blue, amylopectinpurple and proteins yellow. Fats are uncolored. A Nikon FXA microscopeis used to examine the sections and a differential interference contrastis used to increase the contrast in protein stains. The structure of allproducts are similar except that the samples of product 1 indicateinteraction between the chitosan and the proteins and amylose.

EXAMPLE 2

The process of example 1 is repeated except that tvo different mixtureswith different meat, fat and water contents are prepared. Also, prior toaddition of the chitosan solution, a polyphosphate (P₂O₇) is added toeach mixture. The components used to produce each gelled emulsionproduct are as follows:

Meat Fat Starch Chitosan Salt Added Product % % % % % P₂O₅ Water % 2 3512 10 0.5 2 0.5 40 3 29 10 8.3 0.4 1.7 0.4 50.2 Control B 35 12 10 — 20.5 40.5 Control C 29 10 8.3 — 1.7 0.4 50.6

The cans are opened and the contents visually inspected. The chunks ofproducts 2 and 3 are well-formed with well defined, clear edges. Littleor no cook out of fat or starch is noticeable. The chunks of controlproduct B and C have less well defined edges. Cook out of fat and starchis readily noticeable.

A sample chunk is taken from each product and analyzed using a Instron1122 machine at a constant crosshead speed of 20 mm per minute. Thestress and strain values obtained are as follows:

Stress at fracture Strain at Product (kPa) fracture 2 6 0.12 3 3.5 0.137Control B 3.8 0.150 Control C 2.8 0.142

The control product C was too weak and watery to measure the stress andstrain. Products 2 and 3 have a higher stress value than the controlproduct of corresponding water content indicating that they are firmer.Further, the control products have a higher strain value than theproduct 2 and indicating that the control products are more elastic. Itis also noted that product 2 has higher stress and strain values thanproduct 1 of example 1, indicating a synergistic effect between thechitosan and the polyphosphate.

A further sample chunk is taken from each product and the structureanalyzed as described in example 1. The structure of control products Band C is made up of fragments of muscle fibers and a network of muscleproteins surrounding starch granules and fat. The structure of products2 and 3 is very different and is made up of a protein network reinforcedby chitosan surrounding starch granules and fat. The chitosan appears tocross-link to the polyphosphates which are integrated into the proteinstructure.

EXAMPLE 3

The process of example 1 is repeated except that cod fillet is usedinstead of meat, vegetable oil instead of pork fat, and potato starchinstead of wheat starch. Further, two different mixtures with differentfish, fat and water contents are prepared. The components used toproduce each gelled emulsion product are as follows:

Fish Oil Starch Chitosan Salt Added Product % % % % % Water % 4 50 4 100.5 2 33.5 5 45 3.6 9 0.45 1.8 40.15 Control D 50 4 10 — 2 34 Control E45 3.6 9 — 1.8 40.6

The gelled emulsion products are cut into chunks and filled into canswith water. The cans are sealed and sterilized at 121° C. for 20minutes. The cans are then allowed to cool.

The cans are opened and the contents visually inspected. The chunks ofproducts 4 and 5 are well-formed with well defined edges. Little or nocook out of fat or starch is noticeable. The chunks of control product Dand E have less well defined edges. Cook out of fat and starch isreadily noticeable.

A sample chunk is taken from each product and analyzed using a Instron1122 machine at a constant crosshead speed of 20 mm per minute. Thestress and strain values obtained are as follows:

Stress at fracture Strain at Product (kPa) fracture 4 8.4 0.09 5 5.80.09 Control D 6.1 0.115 Control E 5.2 0.105

Products 4 and 5 have a higher stress value than the control product ofcorresponding water content indicating that they are firmer. However,products 4 and 5 have a lower strain value than the correspondingcontrol product indicating that they are less elastic.

What is clamed is:
 1. A sterilized, gelled emulsion product includingprotein, lipid, carbohydrate and a binder; the binder comprisingchitosan and a food grade polyphosphate.
 2. A sterilized, pet foodproduct comprising chunks of a gelled emulsion product in a liquid, thegelled emulsion product comprising protein, lipid, carbohydrate andchitosan as a binder.
 3. A sterilized, gelled emulsion product accordingto claim 2 which comprises 5% to 15% by weight of protein; 2% to 15% byweight of lipid; and 3% to 15% by weight of carbohydrate.
 4. Asterilized, gelled emulsion product according to claim 2 furthercomprising a food grade polyphosphate as a binder.
 5. A sterilized,gelled emulsion product according to claim 4 in which the food gradepolyphosphate is sodium diphosphate.
 6. A sterilized, gelled emulsionproduct according to claim 5 which comprises 0.05% to 2% by weight ofchitosan and 0.05% to 2% by weight of sodium diphosphate.
 7. Asterilized, gelled emulsion product according to claim 1 in which thefood grade polyphosphate is sodium diphosphate.
 8. A sterilized, gelledemulsion product according to claim 7 which comprises 0.05% to 2% byweight of chitosan and 0.05% to 2% by weight of sodium diphosphate.
 9. Asterilized, gelled emulsion product according to claim 1 which comprises5% to 15% by weight of protein; 2% to 15% by weight of lipid; and 3% to15% by weight of carbohydrate.
 10. A process for producing a sterilized,pet food product, the process comprising: forming an emulsion containingprotein, lipid, and carbohydrate adding a binder, which includeschitosan, to the emulsion; heating the emulsion to above about 65° C. tocause the emulsion to gel; forming the gelled emulsion into chunks;filling the chunks and a liquid into containers; and sterilizing thecontainers at above about 120° C. to provide the sterilized, pet foodproduct.
 11. A process according to claim 10 further comprising, priorthe addition of the chitosan, adding a polyphosphate to the emulsion andcausing the polyphosphate to react with the protein.
 12. A processaccording to claim 11 in which the food grade polyphosphate is sodiumdiphosphate.
 13. A process for preparing a sterilized, pet food product,the process comprising the steps of: providing a chitosan binder;forming an emulsion containing protein, lipid, and carbohydrate; addingchitosan to the emulsion; and adding a food grade polyphosphate to theemulsion.